US Food and Drug Administration (FDA) Commissioner Scott Gottlieb has outlined the agency’s plans to address ways to increase the effectiveness of influenza vaccines, including evaluating the selection of the vaccine-manufacturing process.

Gottlieb says there was a reduced effectiveness of this year’s influenza vaccines against one strain of influenza A, called H3N2. Overall, preliminary vaccine effectiveness reported by Centers for Disease Control and Prevention for H3N2 influenza was 25%. The effectiveness of the vaccine against H3N2 in children six months to eight years of age was 51% this season, but the effectiveness in those 65 years and older was only 17%, and the effectiveness in older children and adults under 65 years of age was even lower, according to the FDA. Comparatively, the data show that overall vaccine effectiveness for H1N1 and influenza B was 67% and 42%, respectively, for all age groups combined. Gottlieb added that this year is not the first time the FDA has seen vaccines be less effective against the H3N2 strain of influenza. 

“As such, we are taking a number of actions to better understand why effectiveness tends to be lower against the H3N2 strain and what we can do about it,” Gottlieb said in a February 26, 2018 statement. “By looking closely at the available data and applying the lessons we learn each flu season to the vaccine development process, we offer the greatest chance of developing vaccines that even more effectively prevent the flu in the future.”

He said that the agency does not think the lower effective rates for the H3N2 virus was due to not matching the correct strains in this year’s vaccine. “Although adapting circulating virus strains for manufacture can lead to differences between the circulating strain and the one used for manufacturing that could affect effectiveness, so far the data we have suggest that the viruses provided by reference laboratories to manufacturers to make this year’s vaccines do reasonably match the circulating flu strains that are causing most of the illnesses, including H3N2,” he said in the agency statement.

He added, however, that part of the consideration in evaluating vaccine effectiveness may relate to the manufacturing process. “These lessons may be applied not only to enhancing the most prevalent process for developing influenza vaccine in eggs, but to considering whether greater investment in alternative processes such as cell-based or recombinant approaches to vaccine development are required,” he said.

In addition, he said that the agency particularly wants to understand why vaccine effectiveness against H3N2 influenza year-to-year tends to be lower than effectiveness against other influenza viruses. Gottlieb says that the FDA is collaborating with the US Centers for Medicare and Medicaid Services (CMS), a federal agency, to use a large database that includes information from four million individuals that were administered the flu vaccine to indicate whether they were hospitalized for influenza or treated with antiviral medications for influenza-like illness. This work, which is still underway, is expected to help the agencies understand why overall effectiveness with both cell-based and egg-based vaccines was less than optimal.

The agency is also evaluating the role of adjuvants in vaccine effectives. “We’re also looking at the difference in effectiveness in people 65 years and older who were vaccinated with high-dose influenza vaccines and adjuvanted influenza vaccines to see if effectiveness was better than in those vaccinated with standard dose vaccines,” Gottlieb said. The adjuvanted influenza vaccine contains an ingredient designed to boost the immune system’s response to the vaccine; high-dose vaccines contain four times as much of the influenza material or antigen as standard vaccines, according to information from the FDA. 

“One theory is that people might require a higher amount of H3N2 antigen to elicit a proper immune response to that particular strain of influenza,” Gottlieb said in his statement. “..[T] he work conducted with CMS shows a preliminary finding that suggests the cell-based influenza vaccine might be somewhat more effective than the egg-based vaccine. We are working to follow up on that finding. We’re also combing through the data to see if there are other reasons for why this season’s vaccines were less effective against H3N2. Our scientists are currently working internally and collaborating with others inside and outside of the federal government to understand all of these findings.”

The composition of next season’s flu vaccines will be the subject of an FDA advisory committee meeting March 1, 2018. Every year, the FDA convenes a panel to consider the recommendations made by the World Health Organization (WHO) regarding the composition of influenza vaccines for the Northern Hemisphere, and the WHO helps the FDA select strains for next season’s flu vaccines in the US. The WHO has recommended changing two of the strains currently contained in this year’s influenza vaccines for the Northern Hemisphere.

Source: FDA